A conventional skateboard generally includes a deck with two trucks connected to an underside of the deck and each truck includes an axle with a roller on each end of the axle. The trucks each include a tubular case in which the axle is received and when the skateboard performs a grinding action on rails or other objects, the tubular case grinds on the rails or the other objects. The case has to be strong enough to bear the impact force and the grinding friction, or the case may be deformed and affect the alignment of the axle. If the axle directly grinds on the rail at one end, the axle could be deformed. If either the tubular case or the axle is deformed, the whole truck has to be replaced with a new one. In order to have smooth grinding, users wax the underside of the deck and the tubular case, however the wax is quickly removed.
The present invention intends to provide a grinding assistance device for a skateboard and includes a rolling shaft connected to each truck and the rolling shaft rolls on rails or objects when the skateboarders grind their skateboards.